Highly syndioselective coordination (co)polymerization of isopropenylstyrene

Abstract

Coordination (co)polymerization of para-isopropenylstyrene (pIPSt) and meta-isopropenylstyrene (mIPSt), initiated by scandium (Sc) based catalysts, afforded new type of products, bearing pendant isopropenyl groups with perfect syndiotacity (rrrr > 99%). Sc catalysts demonstrated overwhelming chemoselectivity towards the vinyl group over the isopropenyl moiety of isopropenylstyrene. Compared to the constrained-geometry Sc catalysts, having electron-donating pyridyl methylene fluorenyl ligands Flu′CH₂Py (1, Flu′ = C₁₃H₈; 2, Flu′ = 2,7-^tBu₂C₁₃H₆, Py = C₅H₅N), the half-sandwich Sc catalysts containing electron-withdrawing substituents [3, C₁₃H₈SiMe₃Sc(CH₂SiMe₃)₂(THF); 4, C₅Me₄PhSc(CH₂C₆H₄NMe₂-o)₂] showed much higher catalytic activity under identical conditions. The activity of 4 could be over 2164 kg mol_Sc⁻¹ h⁻¹ at room temperature at a lower monomer concentration (1 mol L⁻¹). Moreover, copolymerization of pIPSt and styrene (St) proceeded fluently in a pathway close to ideal copolymerization, with closely matched monomer reactivity ratios: r_pIPSt = 1.05, r_St = 0.83. Therefore, a series of statically random copolymers with pendant unsaturated olefinic groups, ranging from 5% to 90%, were accessed. These pendant isopropenyl groups could be readily converted into epoxide and bromide moieties at mild reaction conditions.